The Gunners became the first English side to win in the Westfalenstadion after the Wales international continued his run of form with the only goal in the 62nd minute.
"It was a great achievement from the lads," Ramsey told Sky Sports.
"It is always a difficult place to come. We realise that from the last time we came here and drew 1-1.
"They got to the final last year and were unlucky and they are a strong team so we had to do our defensive work.
"We were very good defensively even thought we didn't have any shots in the first half and they had a few, even if it was from distance.
"We kept our shape really well, we were patient and it was a proper away performance from the lads and we got them on the counter-attack."
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